The present invention relates to digital video communication, and more particularly to the insertion of advertisements and the like into a digital video stream. The invention is also applicable to the grooming of digital video streams, such as for recombining selected programs from one or more sources.
The process of inserting advertisements into video programming became much more complex after the transition from analog video to compressed digital formats such as MPEG-1 and MPEG-2. Instead of substituting analog waveforms (or digitized pixels) from one signal to another, it became necessary to first identify a suitable exit point in a first compressed digital stream, and then to align this exit point with a suitable entrance point into a second compressed digital stream. In addition, many parameters needed to be added, modified, or replaced, in order to maintain seamless continuity during the splicing transition. In fact, most digital splicing products in existence today will not only modify these parameters, but will also regenerate the entire stream. This is done to insure that the data rate of the resulting stream remains within the limits of the communication channel used to convey the signal from the splicer to one or more receiving devices. This data rate modification process is often referred to as transrating. The combination of splicing and transrating capabilities is particularly advantageous in products designed not only for ad insertion, but for grooming as well.
Grooming refers to the recombination of selected programs from one or more sources. It is an application which typically depends on transrating to match the combined rate of the selected programs with the data rate of the communications channel. In this case, if changes are made to the selection of programs, or if advertisements are inserted into one or more of these selected programs, then the transrating process will automatically insure that the capacity of the communication channel is never exceeded.
In some applications, the use of transrating may not be justified or even possible. For instance, transrating cannot be applied to encrypted digital programs. In other cases, the programs may be in the clear (not encrypted) and the data rate may be constant and known in advance. Furthermore, it may be known that the capacity of the communications channel is sufficient to accommodate a fixed number of these constant bit rate programs. Normally, in such circumstances it would be safe to assume that there is no need for transrating. The problem, however, is that data rate spikes can be introduced when substituting alternative content into one or more programs, even though the data rate of the new content may be constant and of the same rate as the content it replaces. To understand these transient rate variations, it is useful to model the fullness of the buffer which exists in the receiving devices used to decode and reproduce the video and audio signals.
FIG. 1A shows the fullness of the receiver buffer while receiving a first stream 10 and FIG. 1B shows the fullness of the buffer while receiving a second stream 12. FIG. 1C shows the resulting buffer fullness after a splicer implements a transition from the first stream 10 to the second stream 12. As can be seen, the transition is initiated at the end of the first stream (“Stream 1”) and continues with the beginning of the second stream (“Stream 2”). Note that the buffer becomes empty shortly after the splice occurs, causing the decoder to be starved of data as indicated by the cross-hatched area of the combined stream 14. The result is a disruption in the presentation of video (or audio). In this case, it is due to the nearly empty state of the buffer at the end of Stream 1, followed immediately by a high drain rate at the output of the buffer starting at the beginning of Stream 2.
Transrating could have prevented this disruption by reducing the data rate of Stream 1 just prior to the splice point and by continuing to reduce the data rate of Stream 2 immediately after the splice was executed. However, the cost of transrating implementations applicable to advanced compression formats can be quite high, and it would be advantageous to avoid this cost even in cases where the streams are in the clear and the transrating option still exists. An example of such an advanced compression format is the H.264 video compression standard, which is equivalent to MPEG-4 Part 10, or MPEG-4 AVC (for Advanced Video Coding). MPEG stands for the Moving Picture Experts Group, which has promulgated a set of standards for the compression of digital video and audio data as well known in the art.
It would be advantageous to provide an alternative to transrating that is well suited to applications involving the insertion of advertisements into encrypted programs. It would be further advantageous to provide such a system and methods that involve preconditioning of alternate content, such as an ad, and can be applied either at the time of content origination at the encoder, or at a later time using an independent off-line process. It would be still further advantageous if once processed, the alternate content (e.g., ads) could be encrypted if necessary. It would also be advantageous if the network streams (e.g., video programming) into which the alternate content is to be inserted do not need to be modified and can be assumed to be encrypted. The present invention provides systems and methods having these and other advantages.